Immersion heater



Phl' 7, 1939. J. D. MORGAN" IMMER S ION HEATER Filed May 25, 1937 ATTORNEY UN1TED STATES PATENT OFFICE INIMERSION HEATER John D. Morgan, South Orange, N. J., assignor to Power Patents Company, Hillside, N. J., a corporation of Maine Application May 25, 1937, serial No. 144,604

6 Claims.

The present invention relates to electrical heating devices and more particularly to those devices that are immersed in liquids for the purpose of heating the same.

Heretofore many immersion type electrical heaters have been developed that employ the use of a heating coil wound upon a mica or porcelain core and then enclosed in a metal casing or jacket. Heaters constructed in that manner have been found objectionable because in many cases the metal container in which the heating core is encased cannot be brought into direct contact with certain liquids that are to be heated.

Another objection to the use of such heaters is that the heating elements easily yield to the corroding effect of the liquid where the element is in direct contact with the liquid for any appreciabl length of time. l Another objection to the heaters in use at the present time is that the heating elements are embeddedv in dielectric binders that possess a low heat conductivity coefficient, With the result that it takes an appreciable length of time in which to heat a given amount of liquid.

An object of the present invention is to provide an immersion heater with a metallic heating element embedded in a dielectric material of high heat conductivity.

Another object of the invention is to provide an immersion heater in which the dielectric material in which the heating element is embedded is not in direct contact with the liquid to be heated, thus reducing all possibility of corrosion of the parts by the liquid.

Another object of the invention is to provide an immersion heater with a dielectric embedding material and a glass envelope which surrounds velope will not shatter or crack upon a suddenrise in temperature of the heating element.

Another object of the present invention is to provide a heater that has no metal parts in contact with the liquid to be heated.

With the above and other objects and features in view the invention comprises the improved immersion heater hereinafter described and more particularly defined by the accompanying claims.

The heater herein described is one that has particular application as an immersion heater of the type used by doctors and dentists for sterilizing the instruments used in their practice, but it is to be' understood that the invention is not limited to that type of heater, as the heater can be made into any shape or size to fit any particular need or application.

The Various features of the invention are illustrated in the accompanying drawing in which:

Fig, l is a view of the heater immersed in a receptacle of water or other liquid to be heated.

Fig. 2 is a cross sectional View of the heater; and

Fig. 3 is a longitudinal sectional view of a modified form of heater permanently mounted in a heating receptacle.

Referring more particularly to the drawing, Fig. 1 shows the preferredy type of heater l0 submerged in a container I2 that is partly filled with Water or other liquid. Resistor i4 which serves to heat the fluid, is embedded in dielectric carrier I6. The preferred refractory dieletric carrier is made up of a mixture of substantially parts by weight of ferrosilicon, 40 parts of milled grain Zircon and 6 parts of phosphoric acid. This refractory has the desirable property of being able to be hand molded and shaped and can be readily bonded to the glass casing in which it is enclosed. The zirc0n-ferrosilicon refractory described above has a thermal conductivity better than that of steel. Because of the close contact between the glass casing and the refractory embedding material, the loss in heat transfer is negligible. The refractory in which the heating element is embedded has a coeicient of thermal expansion approximately .0000025.

Dielectric carrier I6 is encased in an envelope I8 that is preferably composed of a nonporous material such as glass or fused quartz having a coeilcient of thermal expansion approximately the same as that of the dielectric material I6.y The casing therefore is preferably composed of Pyrex type glass, that is a glass composed of a mixture of the oxides of boron and silicon, having a coefficient of thermal expansion of approximately .0000032. The dielectric carrier I6 and casing I8 may be physically bonded so that the resistor I4 is in very close contact heat conductivity relationship With the outer shell, being separated merely by the layer of refractory in which it is embedded. It can be readily understood that the resistor element should be positioned as close to the outer shell as possible so that a 'very effective transfer of heat to the outer shell and liquid can be accomplished.

Lead wires 20, 2U' are conducted from the dim electric carrier into a'glass extension tube 2| that is phys1cally bonded to the top of the heater at a point where the lead wires can be assembled for introduction into the tube. Within the tubing 2 I, the lead wires are enclosed in a flexible cable 22 that is provided with electrical terminals (not shown) adapted to make proper electrical connections'to'a source of current in a manner wellknown to the art.

Fig. 3 shows an immersion heater .embodyingr the basic features of my invention showing another type of construction. In this adaptation of the invention, the heater is mounted in 'the side of the vessel or receptacle containing the liquid to be heated. The receptacle has a threaded opening on any one side into which 'the threaded nipple 24 can be screwed. Bushing 28 that ls slotted to receive the lead wires is set within the nipple 24. The outer shell I8 of the heater can be rigidly fixed into the nipple by cementing or other known means. In order to assure a continuous dow of convection currents through and around the heater, casing I8 is perforated with one or as many openings 25 as desired to allow liquid to complete a continuous ilow through the openings.

An immersion heater employing all lof the features hereinabove disclosed has been made and put into use. The resistor employed was #22 gauge wire. Pyrex glass having a thickness of 312 inch was used as the casing `for the embedding material. The heater was equipped with a 1000 watt element and connected to a 115 volt line. Upon test it was found that it required but five minutes to bring one quart of Water to boiling temperature. As shown in Fig. 1, the heater lwas so constructed that both ends are open to` facilitate the rapid heating of the water. Convection currents of the heated water from the bottom of the heater to and through the open top will cause additional cold water to be drawn through the heater. In this manner a continuous flow of liquid through and around the tube'is eected.

By the use of the glass tube leading from the.

edge of the heater to above the surface oi' the water at no time is there any metal or electrical lead oif wires in direct contact with the water or liquid to be heated. This feature of my invention enables one to use the heater in liquid that ordinarily might be chemically affected by contact with metal or rubbercovered wires. For example, the heater can be used for heating liquid foods of vall kinds. It is also ideally adapted for sterilization purposes where utmost cleanliness of the boiling solution is of prime importance.

While I have described one particular modi' fcation of the invention, it is to be understood that the heater can be made in any desirable shape or size.

The length, bore and outside diameter of the heater can be made variable dependent. upon the use to which the heater will be subjected.

The resistor used as the heating element may also depend upon the use to which the heater will be applied. Platinum or tungsten elements can be used where high temperatures are required. Carbon or nickel chromium alloys can be used when low temperature heating is needed.

While Iv have described an immersion heater that isv made up of Pyrex type glassor fused quartz vas the material to be used for the outer covering, I do not so limit the invention. I have also found it suitable to utilize a metal casing which can be used where the utmost cleanliness of the liquid is not of the rst importance provided the metal has the proper ycoeflicient of expansion. One type of metal that can be used as a casing is a metal such as invarr thatis, a metal alloy composed of two thirds iron and one third nickel and small traces of carbon.` This alloy was found to have a coeicient of thermal expansion only slightly higher than that of the dielectric carrier in the temperature range used for heating liquids.

Having thus described theinvention, what is claimed as new is:

l. An electric immersion heater comprising a resistor embedded in a dielectric carrier of high heat thermal conductivity composed of a bonded mixture of Zircon, ferrosilicon and phosphoric acid, said dielectric carrier being enclosed in and bonded to a casing of desired shape that has a coefficient of thermal expansion approximately the same as that of the dielectric.

2. An electric immersion heater comprising a resistor embedded in a dielectric carrier of high heat thermal conductivity composed of a bonded mixture of zircon, ferrosilicon and phosphoric acid, said dielectric carrier being enclosed in and bonded to a glass envelope of desired shape that has a coeflicient of thermalexpansion approximately the same as that of the dielectric.

3. An immersion heateras described in claim l in which the dielectric is composed of a mix- -ture of 60 parts of ferrosiliconby weight, 40 parts of zircon, and 6 parts of H3PO4.

A. An immersion heater as described in claim 2 in which the glass comprising the envelope is composed of a mixture of the oxides of boron and silicon adapted to give a coeiilcientof expansion substantially equal to that of the dielectric.

5. An electric immersion heater comprising a resistor embedded in a dielectric carrier of high heat thermal conductivity composed `of forty parts by weight of milled grain zircon, sixty parts by weight of ferrosilicon, and six parts of phosphoric acid bonded to produce a refractory having a coeilicient of thermal expansion of approximately 0000025, said dielectric carrier being enclosed in a casing of desired shape that has a coeiiicient of thermal expansion approximately the same as that of the dielectric.

6. An electric immersion heater comprising a resistor embedded in a dielectric carrier of high heat thermal conductivity composed oi.' a bonded mixture of Zircon, ferrosilicon and phosphoric acid, said dielectric carrier being enclosed in a casing of desired shape that has a coefficient of thermal expansion approximately the same as that of the dielectric.

JOI-IN D. MORGAN. 

